Senator Chuck Schumer (D., N.Y.) promised that passage of the Gang of Eight immigration bill would render illegal immigration “a thing of the past.” But the Congressional Budget Office report tells a very different story: It projects that 4.8 million new illegal immigrants and their U.S.-born children will be living in the country in 2023 if the bill becomes law. While that represents a modest reduction from the number expected under existing law, it does not even come close to ending illegal immigration but envisions millions more illegal immigrants — a built-in constituency for yet another amnesty a decade hence.

Nor do the projections get any better in the out years. The law would see 7.5 million new illegal immigrants in the decade from 2023 to 2033 — also a modest reduction from current expectations, but hardly a solution to the problem of illegal immigration. High levels of illegal immigration will persist not only because of what the bill fails to do on border security but also because aspects of it will actively encourage future lawbreaking. For example, the CBO forecasts a spike in the number of people illegally overstaying visas issued under new programs for temporary workers.

Perhaps Senator Schumer is one-third correct: Illegal immigration is a thing of the past; it is a thing of the present and, under this bill, would be a thing of the future, too. In fact, the CBO estimates that over the next 20 years we would in effect replace our 11 million or so illegal immigrants with more than 12 million new ones.

It is no wonder, then, that supporters of the Senate bill have focused on the trivial fiscal piece of the CBO report, which concludes that folding in millions of new taxpayers and their attendant economic activity would result in slightly lower deficits and higher economic growth. To get to that conclusion, CBO incorporates some questionable assumptions, the most significant being that measures to exclude newly legalized illegals from government benefits will survive the political pressure that will instantly be focused on repealing them. But even if CBO’s estimates hold true, we are talking about a cumulative deficit reduction of approximately 3 percent a decade hence under current projections. There are better and easier ways of achieving that kind of deficit reduction.

The report’s economic assumptions are grounded in historical experience with far lower levels of immigration — both legal and illegal — than the Senate bill envisions. Whether those assumptions will hold under the radically expanded immigration levels contemplated by the Gang of Eight is unknown. And though neither the CBO nor the bill’s supporters have emphasized the fact, this predicted population influx, unprecedented in its scale, is both the most consequential and the most confounding finding of the report.

The CBO foresees a net increase of 10.4 million legal immigrants through 2023 as a result of the Senate bill. That is 10.4 million on top of the 10 million expected under current law. Add to this 4.8 million new illegal immigrants and the United States could be looking at the introduction of more than 25 million new immigrants in the next ten years. There has simply never been immigration on this scale in this country. The CBO doesn’t specify its assumptions about the distribution of skill levels of these immigrants — saying only that “a greater number of immigrants with lower skills than with higher skills would be added to the workforce” — the categorical breakdown of the influx (“family-based,” “employment-based,” “merit-based,” and other categories of immigrants) suggests a heavy weighting toward low-skilled immigrants.

There is simply no empirical evidence in which to ground any meaningful projections about the economic effects of a flood of low-skilled workers this size into a modern technological economy with a large and growing welfare state. For that reason, no such assumptions are incorporated into the CBO’s fiscal projections, which are drawn instead from our experience with a far more modest pace of immigration. Nor does the CBO specifically differentiate between economic benefits accrued by new immigrants and economic benefits accrued by people already here. But it does find that even with stronger economic growth the bill would decrease the wages of working Americans, and especially the least well off, in the near term. That suggests that the main beneficiaries of this bill are not the current citizens of the United States but citizens of other countries. Congress’s duty is to look after the interests of the American polity, not to engineer a new one.

Far from being the slam dunk some of its supporters claim it to be, the CBO report suggests that the Gang of Eight bill would not solve the problem of illegal immigration but instead would only reinforce the precedent for “solving” it again in the future via the magic wand of yet another amnesty. The economic picture is nowhere near as rosy and unambiguous as the headlines would suggest. Rather, the bill delivers new immigrants, legal and illegal, to America’s shores at a pace and scale unheard of even in the sepia-toned heyday of Ellis Island in exchange for the promise of a rounding-error’s worth of deficit reduction ten years and several elections down the road. And that’s the best-case scenario. Which makes the passage of this bill the worst-case scenario for immigration reform, or something quite close to it.